A republic of southeast Europe on the northern Balkan peninsula. Serbs settled the region in the 6th century and formed an independent kingdom in the 13th century. Dominated by the Ottoman Empire after 1389, Serbia did not regain its independence until 1878. The new kingdom of Serbia expanded its territory during the Balkan wars (1912-1913). After the assassination (1914) of Archduke Franz Ferdinand by a Serbian nationalist, Austria-Hungary declared war on Serbia, sparking World War I. In 1918 Serbia became a major constituent of the Kingdom of the Serbs, Croats, and Slovenes, which was later (1929) renamed Yugoslavia. After the disintegration of Yugoslavia in the 1990s, Serbia remained united to Montenegro until 2006, when the two became separate republics.